WEDNESDAY, Dec. 14 (HealthDay News) -- Less may be more when it comes to blood transfusions after surgery.

New research shows that such transfusions did not speed recovery or reduce the risk of dying among more than 2,000 elderly people who had hip surgery.

More than 15 million units of blood are transfused in the United States each year, often to elderly patients recovering from surgery. Many doctors are starting to use less blood after surgery, but whether or not this practice was safe and in whom was not known until now.

The study, which appears online Dec. 14 in the New England Journal of Medicine, may help reshape how and when blood transfusions are given to patients as they recover from surgery.

Some patients were assigned to a "liberal transfusion" group. They received blood transfusions if their hemoglobin was less than 10 grams per deciliter of blood. Others were placed in a "restrictive transfusion" strategy, and were given blood if their hemoglobin dropped below 8 grams per deciliter. Even individuals in the restrictive group received a blood transfusion if they showed symptoms of blood loss including chest pain, heart failure or unexplained excessive heart rate. Forty percent received blood based on their symptoms.

Hemoglobin is the main component of red blood cells. Its job is to carry oxygen throughout the body. Levels should be greater than 12 to 13 grams per deciliter of blood. Low hemoglobin levels after surgery suggest that blood loss has occurred. As a result, many surgeons will order blood transfusions based on these levels.

Thirty to 60 days after surgery, there were no differences in the ability to walk without assistance or the rate of death or heart attacks seen among the patients regardless of which group they were placed in. Individuals in the liberal group got nearly three times as much blood as those in the restricted group, the study showed.

The study only included elderly patients with underlying heart disease or risk factors, because this population is considered high risk.

The findings provide "further momentum to push down the amount of blood patients are receiving after surgery," said study author Dr. Jeffrey Carson, a professor of medicine at Robert Wood Johnson Medical School in New Brunswick, N.J. "If you can't demonstrate more blood is effective in this high-risk population, then it is highly unlikely to be more effective in lower-risk groups," he said. The findings may not hold for other populations, such as people who have surgery following a heart attack, he added.

"We are better off giving less if we can show more isn't benefiting people," he said. The main reasons for transfusing less frequently include cost and limited supply. "The more you give, the more you spend," he says. There are also times of the year when the U.S. blood supply is tight, he said.

Dr. Tad Mabry, an orthopedic surgeon at the Mayo Clinic in Rochester, Minn., said many surgeons have been waiting with bated breath for a study like this.

"As we have become more and more restrictive, we have had concerns that by withholding transfusions, we may be causing some sort of harm," he said. "It doesn't look like there is any harm to keeping a more restrictive transfusion protocol."

Still, nothing is written in stone. "The power of this study is to say that if you have a patient who has risk factors for heart attack and is not having any anemia symptoms, there is no reason to give blood to get a number up on a lab test," he said. "We can safely wait until the hemoglobin drops to eight."